Diagnosis apparatus and method for an exhaust gas recirculation unit of an internal combustion engine

Abstract

A difference is obtained between a cylinder pressure during the compression stroke when an exhaust gas recirculation control valve is opened, and a cylinder pressure during the compression stroke when the exhaust gas recirculation control valve is closed. An estimated value for this difference is set from a cylinder pressure detected under the closed conditions and an exhaust gas recirculation proportion. When the difference is smaller than the estimated value, it is assumed that the exhaust gas recirculation quantity is not changing in accordance with open/close control, and the occurrence of a fault in the exhaust gas recirculation unit is thus judged.

What is claimed is: 
     
       1. A diagnosis apparatus for an exhaust gas recirculation unit of an internal combustion engine wherein a portion of the exhaust gas is recirculated back to an intake system via an exhaust gas recirculation passage in which is disposed an exhaust gas recirculation control valve, said apparatus comprising: a cylinder pressure sensor for detecting a cylinder pressure of the engine;   cylinder pressure sampling means for sampling the cylinder pressure detected by said cylinder pressure sensor within a pre-set crank angle during a compression stroke; and   diagnosis means for outputting a diagnosis signal indicating the presence or absence of a fault in said exhaust gas recirculation unit, based on the cylinder pressure sampled by said cylinder pressure sampling means and an open/close condition of said exhaust gas recirculation control valve for when said cylinder pressure was sampled.   
     
     
       2. A diagnosis apparatus for an exhaust gas recirculation unit of an internal combustion engine according to claim 1, wherein said diagnosis means outputs a diagnosis signal indicating the presence or absence of a fault in said exhaust gas recirculation unit based on a difference between a cylinder pressure sampled with said exhaust gas recirculation control valve open, and a cylinder pressure sampled with said exhaust gas recirculation control valve closed. 
     
     
       3. A diagnosis apparatus for an exhaust gas recirculation unit of an internal combustion engine according to claim 2, wherein said diagnosis means sets an estimation value for said difference based on an exhaust gas recirculation proportion and the cylinder pressure sampled by said cylinder pressure sampling means, and judges a fault in said exhaust gas recirculation unit when said difference is equal to or less than said estimation value, and outputs a diagnosis signal indicating the occurrence of a fault. 
     
     
       4. A diagnosis apparatus for an exhaust gas recirculation unit of an internal combustion engine according to claim 2, wherein said diagnosis means outputs said diagnosis signal to indicate the presence or absence of a fault based on a difference between a cylinder pressure sampled by said cylinder pressure sampling means during said compression stroke with said exhaust gas recirculation control valve open and a cylinder pressure sampled by said cylinder pressure sampling means during said compression stroke with said exhaust gas recirculation control valve closed, thus avoiding an influence of combustion fluctuations on the diagnosis. 
     
     
       5. A diagnosis apparatus for an exhaust gas recirculation unit of an internal combustion engine according to claim 2, wherein said diagnosis means computes an average value of said difference and outputs a diagnosis signal indicating the presence or absence of a fault in said exhaust gas recirculation unit based on said average value. 
     
     
       6. A diagnosis apparatus for an exhaust gas recirculation unit of an internal combustion engine according to claim 5, wherein said diagnosis means changes a dead zone for fault judgment, based on a number of difference data used during computation of said average value. 
     
     
       7. A diagnosis apparatus for an exhaust gas recirculation unit of an internal combustion engine according to claim 1, wherein said diagnosis means outputs said diagnosis signal based only on the cylinder pressure sampled during a compression stroke, thus avoiding an influence of combustion fluctuations on the diagnosis. 
     
     
       8. A diagnosis apparatus for an exhaust gas recirculation unit of an internal combustion engine according to claim 1, wherein said cylinder pressure sampling means samples the cylinder pressure within a range from 30° BTDC˜20° BTDC. 
     
     
       9. A diagnosis apparatus for an exhaust gas recirculation unit of an internal combustion engine according to claim 1, wherein said cylinder pressure sampling means computes an average value of the cylinder pressure sampled in a pre-set crank angle range during the compression stroke, and said diagnosis means carries out diagnosis based on said average value of the cylinder pressure. 
     
     
       10. A diagnosis apparatus for an exhaust gas recirculation unit of an internal combustion engine according to claim 1, wherein said cylinder pressure sampling means computes an integral value of the cylinder pressure sampled in a pre-set crank angle range during the compression stroke, and said diagnosis means carries out diagnosis based on said integral value of the cylinder pressure. 
     
     
       11. A diagnosis method for an exhaust gas recirculation unit of an internal combustion engine wherein a portion of the exhaust gas is recirculated to an intake system via an exhaust gas recirculation passage in which is disposed an exhaust gas recirculation control valve, said method including: sampling the cylinder pressure detected by a cylinder pressure sensor in a pre-set sampling timing during a compression stroke, and outputting a diagnosis signal indicating the presence or absence of a fault in said exhaust gas recirculation unit based on the sampled cylinder pressure and an open/close condition of said exhaust gas recirculation control valve for when said cylinder pressure was sampled.   
     
     
       12. A diagnosis method for an exhaust gas recirculation unit of an internal combustion engine according to claim 11, wherein a diagnosis signal indicating the presence or absence of a fault in said exhaust gas recirculation unit is output based on a difference between a cylinder pressure sampled with said exhaust gas recirculation control valve open, and a cylinder pressure sampled with said exhaust gas recirculation control valve closed. 
     
     
       13. A diagnosis method for an exhaust gas recirculation Unit of an internal combustion engine according to claim 12, wherein an estimation value for said difference is set based on an exhaust gas recirculation proportion, and said sampled cylinder pressure, a fault in said exhaust gas recirculation unit is judged when said difference is equal to or less than said estimation value, and a diagnosis signal indicating the occurrence of a fault is output. 
     
     
       14. A diagnosis method for an exhaust gas recirculation unit of an internal combustion engine according to claim 12, wherein said step of outputting a diagnosis signal comprises outputting said diagnosis signal to indicate the presence or absence of a fault based on a difference between a cylinder pressure sampled during said compression stroke with said exhaust gas recirculation control valve open and a cylinder pressure sampled during said compression stroke with said exhaust gas recirculation control valve closed, thus avoiding an influence of combustion fluctuations on the diagnosis. 
     
     
       15. A diagnosis method for an exhaust gas recirculation unit of an internal combustion engine according to claim 12, wherein an average value of said difference is computed and a diagnosis signal indicating the presence or absence of a fault in said exhaust gas recirculation unit is output based on said average value. 
     
     
       16. A diagnosis method for an exhaust gas recirculation unit of an internal combustion engine according to claim 15, wherein a dead zone for fault judgment is changed, based on a number of difference data used during computation of said average value. 
     
     
       17. A diagnosis method for an exhaust gas recirculation unit of an internal combustion engine according to claim 11, wherein said step of outputting a diagnosis signal comprises outputting said diagnosis signal based only on the cylinder pressure sampled during a compression stroke, thus avoiding an influence of combustion fluctuations on the diagnosis. 
     
     
       18. A diagnosis method for an exhaust gas recirculation unit of an internal combustion engine according to claim 11, wherein the cylinder pressure is sampled within a range from 30° BTDC˜20° BTDC. 
     
     
       19. A diagnosis method for an exhaust gas recirculation unit of an internal combustion engine according to claim 11, wherein an average value of the cylinder pressure sampled in a pre-set crank angle range during the compression stroke is computed, and diagnosis based on said average value of the cylinder pressure is carried out. 
     
     
       20. A diagnosis method for an exhaust gas recirculation unit of an internal combustion engine according to claim 11, wherein an integral value of the cylinder pressure sampled in a pre-set crank angle range during the compression stroke is computed, and diagnosis based on said integral value of the cylinder pressure is carried out.